When Microsoft released its first tablet, the Surface RT, back in October, details on how it sold were hard to come by, but there was no evidence it was a smash. On Saturday, the company released the Surface with Windows 8 Pro — the Surface that runs conventional Windows applications and otherwise behaves like, well, a PC — and the $999 128GB model instantly sold out.

Now, selling out, of course, is not the same thing as selling well: we don’t know how many Surface Pro units have made their way to store shelves yet. In the case of Best Buy and Staples, at least, there are reports that there haven’t been many Surface Pros to buy, period, so selling out doesn’t mean much.

But Matthew Miller of ZDNet writes that around 75 people were ahead of him in a line at his local Microsoft Store to buy Surface Pros, which counts as a throng in my book. (I don’t remember the last time I heard of 75 people lining up to buy a gadget that wasn’t an Apple product or a game console.) And the 128GB Surface Pro is also sold out on Microsoft’s site as I write this.

One thing I’m curious about: as a full-fledged PC, Surface Pro competes far more directly with the core product lines of Microsoft partners such as HP, Lenovo and Acer than the more limited Surface RT does. Surface Pro is already the highest-profile single Windows 8 computer; if it also becomes a best seller, other PC companies will presumably feel it in the pocketbook as it chips away at sales of other PCs. That will tick them off. And that could end up disrupting the PC industry in ways that Surface has not done to date.

The only way we’ll know for sure how Surface is selling is if Microsoft tells us how it’s selling. Even if the company is pleased with sales, it may not be inclined to do that: for one thing, Apple’s million-unit weekends have set the bar of blockbusterhood so high that a product can do really well and still look like a dud compared with the latest iPad or iPhone.

Absent tangible numbers, I’m going to be looking for Surface Pros in the wild — on airplanes, at conferences and other places where people engage in the sort of on-the-fly productivity that it’s designed to enable. If the Surface Pro is a hot product, it’s going to be out there in meaningful numbers.